Asus X556UA Replacement Battery C21N1509 7.6V 5000mAh
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Asus X556UA Replacement Battery C21N1509 7.6V 5000mAh - is backordered and will ship as soon as it is back in stock.
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Battery Care Tips
Battery Care Tips
🔹 Getting Started
Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.
🔹 Keep It Healthy
Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.
Delivery and Shipping
Delivery and Shipping
🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.
Disclaimer
Disclaimer
⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.
🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
Asus X556UA Replacement Battery C21N1509 7.6V 5000mAh - is backordered and will ship as soon as it is back in stock.
Voltage
7.6V
Amp
5000mAh
Asus X556UA Series — 7.6V Li-Polymer Replacement Battery (C21N1509)
This is a 7.6V, 5000mAh (38Wh) Li-Polymer replacement battery for the Asus VivoBook X556 series, including the X556UA, X556UB, X556UF, and X556UJ. It slots into the same bay as the original C21N1509 cell and restores cordless operation when the factory battery can no longer hold a usable charge. Voltage and connector match the original spec exactly.
- X556 series compatibility: The X556UA, UB, UF, and UJ share a common battery bay, connector pinout, and BMS handshake — all confirmed against the C21N1509 spec. The same 7.6V two-cell Li-Polymer configuration runs across the entire sub-series, so one cell fits all of them.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on an X556 board and confirmed the BMS handshake completed without error codes. The BIOS picked up the cell, reported capacity, and charge current stepped down correctly at the top of the charge curve.
- First-cycle reset on the X556: After fitting, let the battery discharge fully until the laptop hibernates, then charge it uninterrupted to 100%. This forces the BIOS battery learn cycle to recalibrate against the new cell and clears the false "poor health" warning that appears after every cell swap on this platform.
Why the X556 BIOS flags a new battery as poor health
The X556 BIOS stores battery health data from the previous cell in EEPROM. When a new cell is installed, that stored data no longer matches the new chemistry profile — so the system flags poor health immediately, even on a brand-new battery. This is a calibration state, not a fault with the replacement cell. Running one full discharge-to-hibernate followed by a complete uninterrupted charge overwrites the EEPROM reference point and resolves the warning.
Laptop shuts down at 20–30% charge shown on screen
This happens when the fuel gauge IC has not yet calibrated to the new cell — it reports a percentage, but the underlying voltage curve it's reading from is still mapped to the old, degraded cell. Under full CPU and display load, the actual cell voltage drops faster than the gauge expects and hits the cutoff threshold early. The fix is two to three full discharge-and-charge cycles, which give the fuel gauge IC enough data to remap its curve to the new cell. After calibration, the gauge and actual remaining capacity align at a consistent voltage floor around 6.0V under load.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: Asus
- Manufacturer: CS
- Series: Standard
- Color: Black
- Product Type: Li-Polymer
- Battery Type: Li-Polymer
- Warranty: 12 Months
- Bulk Orders: sales@batteryweb.com
Frequently Asked Questions
The Asus battery info screen shows the wrong Wh rating after I swapped the battery — is something wrong with the cell?
The Wh figure shown in Windows or BIOS is pulled from the EEPROM data embedded in the battery's BMS chip, which stores the rated capacity at the time of manufacture. The new cell's EEPROM value may differ slightly from what the old cell reported, but this does not mean the physical capacity is wrong — 38Wh is the actual chemistry spec for this cell. Cross-check by running a full discharge cycle and watching the drain in mWh via HWiNFO64; the real delivered energy will align with the 38Wh rating within a cycle or two.
My X556 fuel gauge is jumping around — shows 60%, drops to 40%, then climbs back up without charging
The fuel gauge IC on the X556 platform needs two to three full discharge-and-charge cycles to map its voltage-to-percentage curve against a new cell. Until it has enough data, the reported percentage can jump by 15–20 points under load or during light use. Run the laptop on battery from 100% down to hibernate-cutoff, then charge fully without interruption — repeat this twice more and the gauge will stabilise. After calibration, charge percentage should track smoothly without sudden drops.
New battery installed but the X556 won't charge above 80% — charger is plugged in but it just stops
The X556 BIOS includes a charge limit feature that caps charging at 80% to reduce long-term cell wear — it is firmware-controlled, not a fault with the replacement battery. Check the Asus Battery Health Charging utility in Windows; if it is set to "Balanced" or "Maximum Lifespan" mode, it will stop charging at 80% by design. Switch the mode to "Full Capacity" in the utility and the battery will charge to 100% on the next cycle. If the utility is not installed, download it from the Asus support page for your X556 model.
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